1. Field of the Invention
This invention relates generally to a tape cassette, and more particularly to a tape cassette having a casing which comprises an upper half, a lower half and within which casing a reel is urged toward the lower half. The invention is best suited for applying to a tape cassette for video tape recorders.
2. Description of the Prior Art
Firstly, a conventional tape cassette for video tape recorders (hereinafter described as VTR) will be described with reference to FIG. 1.
In the above tape cassette, a pair of right and left reels 2, on which a magnetic tape 1 is wound and only one of which is shown in FIG. 1, are rotatably accommodated in a cassette casing 5 which comprises an upper half 3 and a lower half 4. Reel pressing means 6 is fitted to a through hole 7 disposed in the upper half 3 so as to be movable in up and down direction, and is urged downwards by the force of a spring 8 which lies between the reel pressing means 6 and the upper half 3. Thus, a semi-sphere-like projection 9 provided at the central lower end of the reel pressing means 6, depresses a metal plate 11 as a bearing which is horizontally fixed to the upper end of a hub 10 of the reel 2 so that the reel 2 is urged toward the lower half 4.
When the tape cassette inserted into a cassette mounting device (not shown), which is provided in the VTR, is conveyed to a position where the tape cassette is mounted, a reel base 13 is relatively inserted from below in an opening 12 which is provided in the lower half 4, and a driving shaft 15 projecting from the central part of the reel base 13 is fitted into a hole 14 which is opened at the central lower end of the hub 10. At the same time, annular ribs 17 projecting from the bottom face of the lower flange 16 of the reel 2 in coaxial relation with the reel 2 abut against the reel base 13, so that the lower flange 16 of the reel 2 is separated upwards from the lower half 4, and at that time, a reel pressing member 18 comprising a leaf spring or the like, and provided in the cassette mounting device, depresses the top end 6a of the reel pressing means 6, so that the reel 2 is firmly fixed to the reel base 13 by the forces of the reel pressing member 18 and spring 8.
Meanwhile, it will be seen that the reel pressing means 6 of the tape cassette has a plurality of vertical slits 19 at the upper end 6a thereof so as to make a plurality of engaging portions 20 capable of elastic deformation. Thus, if the engaging portions 20 of the reel pressing means 6 are inserted from below into the through hole 7 of the upper half 3, the reel pressing means 6 can be connected to the upper half 3.
As a result, the top face 6a of the reel pressing means 6 is of discontinuous surface, so that the reel pressing member 18 of the cassette mounting device is apt to be caught by the reel pressing means 6 when it abuts against the top face 6a of the reel pressing means 6, and thereby, the action of the reel pressing member 18 is made uncertain.
The uncertain action of the reel pressing member 18 makes it difficult to stably fix the reel 2 to the reel base 13, thus the magnetic tape 1 can not run stably due to unsmooth rotation of the reel 2, such as a gyration of the rotation axis of the reel 2 or an irregular movement of the reel 2. Moreover, there are many restrictions to determine the configuration and construction of the reel pressing member 18 so as not to have the reel pressing member 18 caught by the reel pressing means 6.
Instead, if the reel pressing means 6 is constructed so as to be inserted from above into the through hole 7 of the upper half 3, the reel pressing means 6 must come out of the through hole 7 when the reel 2 is pressed upwards by a large force, or the discontinuous surface of the reel pressing means which comes in contact with the bearing 11 of the reel 2, must wear quickly when the reel is rotated.